1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor laser, a semiconductor laser, an optical disc device, a method of manufacturing a semiconductor device, and a semiconductor device, and more particularly, to a ridge stripe-type semiconductor laser having an end surface window structure using a nitride-based group III-V compound semiconductor and an optical disc device using the semiconductor laser as a light source.
2. Description of the Related Art
In order to increase the maximum light output of a semiconductor laser, it is necessary that an end surface window structure be adopted in which a window that is transparent to light from an active layer is provided in a resonator end surface.
In a GaInP-based red light emission semiconductor laser of the related art, there is an effective method of forming an end surface window structure by diffusing Zn atoms in a semiconductor layer close to a portion, which will become the resonator end surface, after growth of a semiconductor layer forming a laser structure so as to locally increase band gap energy (for example, see Japanese Unexamined Patent Application Publication No. 2005-45009).
On the other hand, recently, in a high-density optical disc device or the like, a nitride-based group III-V compound semiconductor-based semiconductor laser has been used as a light source. Most of nitride-based group III-V compound semiconductors are materials which are thermally or mechanically stable, as compared with a GaInP-based semiconductor. To this end, with respect to a nitride-based group III-V compound semiconductor-based semiconductor laser, it is difficult to form an end surface window structure by a diffusion process of heterogeneous atoms and wet etching, which is effective in a GaInP-based red light emission semiconductor layer.
In a nitride-based group III-V compound semiconductor-based semiconductor laser, up to now, there have been proposals and experiments carried out on various methods of forming an end surface window structure. Hereinafter, the methods of forming the end surface window structure proposed up to now will be described.
A method has been proposed for forming an end surface window structure by increasing band gap energy near the resonator end surface using an In elimination phenomenon by H2 plasma exposure or laser beam irradiation after a laser bar is formed by cleavage (for example, see Japanese Unexamined Patent Application Publication Nos. 2006-147814 and 2006-147815). However, since a high-vacuum chamber device is necessary in order to perform such a method, investment in equipment is extensive, and in the processing of the resonator end surface after cleavage, there are generally issues remaining with regard to productivity.
Numerous methods have been proposed for epitaxially growing a semiconductor layer forming a laser structure on a substrate, drilling a portion, which will become a resonator end surface, of this semiconductor layer using Reactive Ion Etching (RIE) and again epitaxially growing a nitride-based group III-V compound semiconductor layer with large band gap energy on that portion (for example, see Japanese Unexamined Patent Application Publication Nos. 2004-134555, 2003-60298, International Publication No. 03/036771, and Japanese Unexamined Patent Application Publication No. 2002-204036). However, in these methods, there is a concern that a surface level is formed on a surface drilled by using RIE and light absorption or local heat generation may occur during a laser operation.
In addition, as another example, a method has been proposed for forming an end surface window structure by epitaxially growing a semiconductor layer forming a laser structure on a substrate in which a geometric step difference is provided by RIE or insulating film deposition (for example, see Japanese Unexamined Patent Application Publication Nos. 2005-191588, 2005-294394, 2003-198057 and 2000-196188). In this method, it is intended that a cladding layer with large band gap energy operate as an end surface window structure compared with an active layer in the traveling direction of a laser beam. A representative example is shown in FIG. 25. As shown in FIG. 25, in this semiconductor laser, one main surface of a substrate 101 is patterned by RIE so as to provide a concave portion 101a, an n-type semiconductor layer 102, an active layer 103 and a p-type semiconductor layer 104 are sequentially grown thereon, and a p-side electrode 105, an isolation electrode 106 and a pad electrode 107 are formed on the p-type semiconductor layer 104. However, such a method has the following problems. That is, since a steep geometric step difference is generated in the n-type semiconductor layer 102, the active layer 103 and the p-type semiconductor layer 104 by the concave portion 101a of the substrate 101, optical waveguide loss occurs in the vicinity of the step difference. In addition, transparency by a wide gap of the active layer 103 near a resonator end surface is not intended and there is a possibility that a valid end surface window structure may not operate.
The present applicant first proposed a method of manufacturing a semiconductor laser having a window structure by forming a mask formed of an insulating film in the vicinity of at least a formation position of an end surface window structure on a substrate and then growing a nitride-based group III-V compound semiconductor layer including an active layer formed of a nitride-based group III-V compound semiconductor including at least In and Ga, in order to solve the drawbacks of the above-described method of forming the end surface window structure of the related art (see Japanese Unexamined Patent Application Publication No. 2008-244423).